Offshore oil drilling platforms and rigs typically utilize surface seawater as the cooling medium for the operational generators that are required to power the rig and support operations. Similarly, offshore liquefied natural gas (LNG) plants and regasification plants traditionally use surface seawater as both a heat sink and a cooling medium. Relatively large flows of water are required to provide the cooling medium necessary to efficiently operate the power and liquefaction systems, respectively. Surface water is typically received for these purposes at 20-30° C. in the tropical and sub-tropical regions (i.e., Gulf of Mexico, South America, and the like). As latitudes increase, the surface water temperatures lower.
In almost all cases, there are occasionally issues with limitations of operation as the intake and discharge are subject to EPA or similar regulations on the chemical, biological, and thermal properties of these resources and return streams. Specifically, in the U.S., EPA regulations 316(a) and 316(b) restrict the temperature elevation limits of the cooling water discharge (316(a)) and the impingement/entrainment characteristics (316(b)) of the cooling water intake. In the Gulf of Mexico and many tropical and sub-tropical locations, this surface water is often the primary region of important commercial fishery larvae and early life-stages that are very sensitive to entrainment into such intake systems due to the fact they have little ability to avoid intake streams and imposed currents. This can put a significant burden and stress on the regional fishery and, hence, has become a sensitive environmental point of contention between offshore drillers, LNG operators, and local fishermen and environmental groups.
The current intake for the aforementioned cooling systems typically occurs at or near depths of productivity maximums. Accordingly, there are clear environmental impacts to uncontrolled cooling water intake and discharge within this biologically sensitive region. In addition, there are potentially significant impacts to localized and regional fisheries for strategic commercial species.
Moreover, the relatively high temperature of the intake waters in some areas (20-30° C.) and the regulations on the return water occasionally require offshore systems to shut down operations on off-design warm days to accommodate and meet the environmental requirements imposed. These shutdowns and delays in operation are costly in any industry, but especially so in offshore operations.
Thus, there remains a need in the art for a system and method to draw cooling water for offshore operations from regions of minimal biological productivity so as to lessen the environmental impact, prevent disruptions of operations, reduce or eliminate biofouling issues in system heat exchangers and improve cost effectiveness of the cooling water resource. In addition, initially cooler heat sink temperatures are needed to improve generator efficiency, reduce operational costs, lower resource water flow rates, lower environmental impact, and improve operational reliability. Obviously, a cooler, less environmentally sensitive cooling water resource would be useful to all stakeholders—oil rig/LNG operators, offshore construction contractors, fishermen, and other environmental proponents.